Yeah Racing (#MR01-150SV) - Rear Damper Set
This is suitable for the Kyosho Mini-Z Racers.
These are located on the back (single reat damper).

It can improve the car's performance on the uneven road, it can absorb shock from the motor mount, so the stability of the car can increase.

There are three set of springs with different tensions in the package.
green: hard
blue: medium
red: soft

On the flat road, it is better to use green one, because it can provide good stability to the car in flat road. On uneven road, it is better to use red one, because it can provide better shock absorption, so the car can be more stable. For the blue one, it is suitable for most road condition, when you don't know the road is flat or not, it is better to use green one.